As mobile Internet becomes pervasive, Location-Based Applications (LBAs) are rapidly adopted by mobile users for always-on contact with friends, business, entertainment, and others. Examples of such LBAs include mobile social-network applications (e.g., Twitter, Facebook), local restaurant, and real-time traffic applications. Furthermore, as open smartphones such as Android phones become available, the more number of location-based applications are being developed.
However, even though smartphones become powerful enough to support various LBAs (e.g., being equipped with new sensors such as Global Positioning System or GPS), they still suffer from limited battery life, hindering the active usage of LBAs. Typical battery capacity of a smartphone today is barely above 1000 mAh (e.g., the lithium-ion battery of HTC Dream smartphone has the capacity of 1150 mAh). Unfortunately, the use of GPS, which is the core of LBAs, is power-intensive, and can cause the complete drain of the battery within a few hours.